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Hi so i went for a mot and the car didnt pass, got the work done but the 10 days retest period has passed, so went somewhere else cheaper thinking the car will pass, but the person i went to is very picky. Among other things that the person picked out is the brake lights staying on slightly, but fully when brake is pressed so i went for the most common, and brought a brake light switch changed it and still the same, took the fuse out and turned the ignition on the lights were still on (dont ask why was checking every possibility even if its daft) also disconnected battery for several minutes to reset the ecu, still same problem and checked rear light cables if theres a short circuit, but looks clean with no splits also disconnected the brake light switch and clutch pedal thingy still same problem, the car is a passat 2000 b5 1,9 dti all suggestions on what causes it is really appreciated.
 

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I've seen this issue often, and it nearly always turns out to be either a failing ground, or incorrect bulbs installed in the taillights.
 

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Since the taillight housing has a common ground, having a compromised or weak ground outside of the housing can indeed cause this issue. The bulb that is being fed B+ will use whatever path to ground it has, and that path, when the external ground is damaged, turns out to be through other bulbs in the housing since they have a common conductor that would normally be at ground potential. It effectively makes the bulbs work in series, causing more than one to light up. I have personally seen and corrected this issue on a number of cars over the years, so I'm speaking from experience.
 

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The OP wasn't very clear in his description, I understood him to say the lights stayed on when no rear lights were switched on.
If this is the case the lights couldn't come on because of a fault of any kind in the rear lights or their ground.
If the stop lights are on and dull, only when some other rear light is on, then the fault would most likely be either a bad ground,
or incorrect bulbs in the taillights.
 
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